Support is requested for a Keystone Symposia meeting entitled HIV Pathogenesis - Virus vs. Host, organized by J. Victor Garcia-Martinez, Daria J. Hazuda and Dan R. Littman. The meeting will be held in Banff, Alberta, Canada from March 9-14, 2014. This meeting will be focused on the latest breakthroughs in basic and translational HIV research with an emphasis on mechanistic models. It will present a detailed tour of all the key steps of virus replication from infection to AIDS. The program seamlessly incorporates key aspects of 1) virus entry/exit into the cell, 2) entry into the host, 3) virus-hos genetics and co-evolution, 4) virus-host interactions and responses, 5) pathogenesis, 6) reservoirs, latency and reactivation, and 7) HIV and the microbiome at the mucosa. Strong emphasis will be given to these and other areas well represented in the abstracts submitted. Opportunities for interdisciplinary interactions will be significantly enhanced by the concurrent meeting on HIV Vaccines: Adaptive Immunity and Beyond, which will share opening and closing keynote addresses and two plenary sessions with this meeting. The topic of this meeting is highly relevant to the NIAID Division of Acquired Immunodeficiency Syndrome's mission to increase basic knowledge of the pathogenesis and transmission of HIV.